IP-in-IP Tunnels

IP-in-IP tunnels are used to forward information between endpoints acting as a bridge between portions of an IP internetwork that have differing capabilities. A typical use for IP-in-IP tunnels is the forwarding of IP multicast traffic from one area of the intranet to another area of the intranet, across a portion of the intranet that does not support multicast forwarding or routing.

With IP-in-IP tunneling, an IP datagram is encapsulated with another IP header addressed to and from the endpoints of the IP-in-IP tunnel, as shown in Figure 4.5. An IP-in-IP tunnel is indicated by setting the IP Protocol field to 4 in the outer IP header. For more detailed information about IP-in-IP tunneling, see RFC 1853.

Figure 4.5 IP-in-IP Tunnel Packet Structure

IP-in-IP Interfaces

An IP-in-IP interface is a logical interface that sends IP packets in a tunneled mode. To create an IP-in-IP interface, in the Routing and Remote Access snap-in, right-click Routing Interfaces, click New , and then click Tunnel (IP only) . After the tunnel is created, add it as an IP routing interface by right-clicking the General node under IP Routing , and then clicking New Interface .

After IP-in-IP interfaces are created and added as an IP routing interface, you must configure the tunnel endpoints. Then, you can configure them the same as any other IP interface, including setting packet filters to confine the traffic that is allowed into and out of the interface, and multicast scopes and boundaries.